


Something fishy is going down here

by OtakusUnite



Series: Down the rabbit hole known as undertail [2]
Category: Undertale (Video Game)
Genre: Eventual Smut, F/M, Porn With Plot, Post-Neutral Route (Undertale)
Language: English
Status: Completed
Published: 2016-04-28
Updated: 2016-04-28
Packaged: 2018-06-04 23:22:39
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,229
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6680056
Author URL: https://archiveofourown.org/users/OtakusUnite/pseuds/OtakusUnite
Summary: <blockquote class="userstuff">
              <p>It had been ten years since Frisk had fallen into the Underground. With the souls and their King gone, the monsters held no more hope. Who would've thought you were the one to bring it to them? And maybe you'll find love along the way.</p>
            </blockquote>





	Something fishy is going down here

**Author's Note:**

  * For [Marschall](https://archiveofourown.org/users/Marschall/gifts).



> Basing this around how Alphys disappeared at the end of the neutral route. The only way I thought this could work if it was post-neutral, since in pacifist the two of them get together. Hope that's ok.
> 
> Also that all monsters are pansexual, and are more likely to fall in love with the soul of a person than their actual features. Since you know, they can actually see souls and all.

**Guide:**  
(F/N) - first name  
(L/N) - last name  
(F/C) - favourite colour

* * *

 

You were screwed. You were so screwed. Laying on the ground, you looked up at the angry fish lady pointing a spear at your face. Maybe you should start from the beginning.

It had been ten years since Frisk had fallen into the Underground. After Toriel had tried to take over from Asgore and failed, everything fell into an uneasy anarchy. Undyne took over, since head of the royal guard was the closest thing to a king they had.

She had declared to kill anymore humans that fell down. She set up patrols everywhere, even in the ruins. And this is where you find yourself now.

Honestly, you had no idea how you even got here. One minute you were hiking on Mt Ebbot, hoping to find a glimpse of your sibling, the next falling down this really steep hole and blacking out. Though there was a small moment when colours flashed in your face and disappeared into your chest, but you played it off as a hallucination before death.

Next thing you know when you wake is a glowing blue spear right up in your face. If it wasn’t for the fact that you probably had a concussion, you’d be shitting your pants right now.

A feral grin took over her face that didn’t match the death glare she gave you. “Well, well, well! What do we have here?!”

You gulped. “Hi…?”

Despite having only one eye, she sure gave you a pretty harsh looked. “Don’t you ‘hi’ me! Don’t you know what your people have done to us? What the little shit before you did?!”

You frowned. “You mean Frisk…?”

The spear tip pressed against your throat just enough to prick the skin. “So you do know them!”

“Only because they were reported missing! Nobody found them, and everyone in the village thinks their dead!”

She blinked, or winked, hell you didn’t know, everything was too confusing as it was. “Wait, they didn’t even make it to the surface? And to think they defeated Asgore. What a whimp!” Her eye narrowed and she pressed the spear in more, drawing a few drops of blood. “Why are you here then?”

“I fell, I swear.”

She rolled her eyes and picked you up by your hair, causing you to curse in pain. “You can tell me the truth when you reach the capital. There you will be publicly executed.”   
“What?! But I haven’t done anything wrong!”

She turned her glare back to you. “That’s the thing, you didn’t have to. It was already done for you.”

Just as you were about to respond, you felt an overwhelming pressure in your chest and passed out, something that shocked Undyne but you couldn’t see.

 

 

When you came too, it was to the sight of a stone room with bars, probably a cell. However, your concentration from was sharply drawn to the extreme pain in your chest. Clawing at it, you tried to call for help, anything, but nobody came. Or so you thought.

The door was kicked in, and the same fish lady from before marched in, some sort of goat creature after her. Both of them gasped in surprise before the goat monster rushed up to you. “Undyne! Why didn’t you get me sooner?”

“I thought he was just faking it!”

The goat monster sent her a glare before putting a hand over your chest. “My child, this will hurt, but I need to check your soul.”

You could barely understand what they was saying, mainly because of the pounding sensation in your ears but nodded anyways. “P-Please..!”

They frowned. “This may feel uncomfortable, my child.”

There was a tug, but nothing compared to the pain you were feeling. A bright glow erupted from your chest, your gasp drowned out by the exclamations of shock from the other two. A (F/C) heart bobbed above your chest, which was confusing enough, but what made it even more so were the seven smaller hearts, ranging the colours of the rainbow, circling around it.

The goat monster seemed to want to reach out to the other hearts but stopped themselves. “U-Undyne….are they..?”

You were suddenly lifted from the bed and pinned to the wall by your throat. “Where the hell did you get these?! And where did you find the seventh?!”

You pawed at her hand, unable to answer due to your throat being constricted. The goat monster seemed to notice and put a hand on her arm. “Undyne, he needs to breathe.”

“But Toriel-!”

“He can’t answer you like that.”

She growled but let go of you, letting you fall back onto the bed. Once you got your breath back you told her everything. About how you were searching the mountain for your sibling. About the colours you saw before blacking out when you fell. About the pain in your chest before you blacked out for a second time.

Toriel and Undyne listened closely, before leaving the room to talk. You could hear hushed arguing, louder on Undyne’s part, as your wondered what the hell was going in. Toriel came back in. “We’ve decided that you can help us, but for now we must keep the souls in you, as they seem to be stable. What’s your name?”

You frowned. “(F/N) (L/N). What are you going to do with me?”

Toriel gave you a gentle, patient smile. “You are going to help us break the barrier.”

 

 

It had been six months after that moment. After a lot of explaining about the souls, and how seven of them can be used to break the barrier that trapped the monsters in the underground. They took you to the capital, and with their guidance, they used the souls to break the barrier.

Despite the fact that the humans actually welcomed them into society, and there were very little riots and outbreaks of violence, a lot of monsters still stayed underground, mainly because that’s what they were used it. It didn’t mean they didn’t go to the surface, but it was more like a holiday trip then they’d be back.

However, you decided to stay with them underground. After finally finding out what happened to your sibling, there was nothing for you on the surface and you had made friends with everyone underground.

Except for Undyne.

You weren’t sure how to feel about her. You had a suspicion that your feelings towards her were more than friendship, but you couldn’t tell how she felt about her. You two had slowly become close friends, as you taught her the truth about humans, and she taught you how to live in the underground and self defense, but she always had this standoff-ish attitude about her whenever you got a bit too close.

And besides, you had seen the look in her eye whenever someone talked about Alphys, who you found out had committed suicide a few months after Frisk, unable to take the pressure of what she’d done. It was the look of someone who had lost the person they cared most about, even if she may not know that she’s doing it. You should know, you had that exact same look for a long time too.

 

 

“Hey, be careful!” You cried out as a spear came a little too close for comfort.

You two were having one of your training sessions, but Undyne just seemed to be letting out her frustrations on you. She glared at you and just kept throwing spears, launching herself at you. Dodging the spears, you blocked her and pushed her off. With every jab of the spear she said another word. “Why! Are! You! So! CONFUSING?!”

You frowned, and blocked her jabs. “What do you mean?”

Undyne growled and summoned a spear in each hand, using them to attack you. “You make me feel strange! Weak!”

You blinked in surprise, getting distracted at what she meant. She noticed and used that to her advantage, knocking you to the ground. Practically straddling your waist, she had pinned your wrists above your head with a smug smirk, which changed to a strange look when she saw your beet red face. “What’s the matter with you, nerd?”

You gulped and tried to calm your racing heart. “W-What did you mean by I made you w-weak..?”

She grumbled. “I dunno. I get all jumpy when we’re by ourselves. I worry about you when I haven’t heard from you. You throw me off my game, and are always on my mind… Is this some sort of magic? Did someone put you up to this, punk?!”

You shook your head. “Of course not! But on the surface, some people call it magic.”

Undyne just looked at you confused. “What the hell are you talking about? I thought humans didn’t know anything about magic.”

You sighed. “Maybe it’s easier if I show you.”

Knowing that you’re life was on the line if you were wrong about this, you leant up and kissed her. She froze in shock as you slowly pulled away. “Some people say that love, the nice kind, can be a sort of magic…”

Undyne was silent, taking it all in while you were lying there scared as hell. Her silence made you afraid that you were wrong, that you stuffed this up and she was never going to want to see you again. What you didn’t expect was for her to lean down and kiss you again.

Once you gained the function to move again, you kissed her back. It was much rougher and desperate than the first kiss you gave her, but you weren’t complaining. Deepening it, you licked her lips, asking for permission. Eagerly opening her mouth, you thrust your tongue into it, entangling her tongue with yours. 

She let out a low growl of approval and pleasure as you sucked on her tongue. Pulling away so you could breathe, you looked up at Undyne, who had a pleased flushed look on her face. She shifted on your lap, causing you to bite your lip. She noticed this and smirked. “Inside?”

You nodded. “Inside.”

You didn’t expect her to pick you up and carry you to her room, though when you think about it, it’s not very surprising. She somewhat gently chucked you onto her bed and straddled your hips against, this time clearly feeling the bulge residing there.

Undyne ground against you, your gasps of pleasure mingling together. You were quick to shed your clothes, Undyne the same. Not that the two of you were wearing many clothes to begin with. She went to kiss you again, but you stopped her reluctantly. “Not that I don’t want to continue, but what are you comfortable with?”

This caused her to stop and think. She just ended up shrugging. “Don’t care to be honest. All I know is that I want to get fucked by you, right here, right now.”

You chuckled and pulled her close, smirking sinfully. “Then what are we waiting for?”

She snorted and grinned. “You, you dork.”

Before you could respond she kissed you again. This time it was filled with furious passion, teeth knocking occasionally, accidentally nipping a bit too hard, but the two of you didn’t care. You felt her take a hold of a member and bring it to her entrance. You were about to say something when she sat down on it, drawing gasps and moans of pleasure out of the two of you.

You rocked up into her, drawing a louder moan out of her. Undyne rested her hands on your chest, and you puts your on her hips. You rocked up again, this time she began to bounce with you, drawing out sounds of pleasure from the both of you.

Alternating her bounces with grinds, you met her bounces with your thrusts. You let her stay in control, just going along with what felt natural. Moans and gasps of pleasure filled the air, making the whole scenario more intimate as they mixed together.

Undyne bounced harder and faster. Rocking up, she let out a cry of pleasure as you hit her g-spot. Smirking, you continued to thrust into it as she bounced, her timing getting more frantic as she was desperate for release. And to be honest so were you.

Sitting up just enough to kiss her, it was a clash of teeth and tongues as you soon reached your ends. It was one hard thrust into her sweet spot that tipped her over the edge. Gripping your shoulder tightly, she yelled out what you thought was your name, but it was hard to tell as you felt her walls tighten around you, making you cry out in pleasure as you reached your peak.

Coming down from your highs, Undyne rested her head on your shoulder. She wasn’t panting as hard as you, but that was a given with how fit she was. You nuzzled her head before letting go of her so she could get off your lap.

You smiled at her once she laid down beside you. “How was it?”

She grinned. “Not too bad for a nerd like you.”   
Chuckling, you lay beside her, taking her hand in yours. “I love you.”

Undyne’s grin turned into something softer. “I love you too, ya big dork.”

**Author's Note:**

> First smut fic, so I apologise if it's bad. Still learning :3  
> And sorry if there's more plot than smut, didn't feel right without a backstory.


End file.
